A gas turbine comprises a compressor stage and a turbine stage. In each stage, respective airfoils, i.e. rotatable blades and stationary vanes, are arranged, which are exposed to a working fluid which streams through the gas turbine. The turbine stages are arranged downstream of a burner of the gas turbine, such that the vanes and blades are exposed to a hot working fluid. Hence, the vanes and blades have to be cooled in order to extend the lifetime.
It is known to install an impingement tube inside a respective airfoil, wherein cooling fluid streams through the impingement tube against an inner surface of the airfoil.
When cooling fluid streams against an inner surface of the airfoil by using an impingement tube, the cooling fluid will take further the path of least resistance along cooling ducts formed between the inner surface of the airfoil and the outer surface of the impingement tube. Hence, if cooling fluid is injected in a nose region of the impingement tube, more mass flow of cooling fluid is flowing through a cooling duct along one airfoil surface than through another cooling duct along an opposite airfoil surface.
FIG. 6 shows a conventional airfoil for a gas turbine which comprises a conventional outer shell 601 and a conventional inner shell 610. A conventional cooling channel 602 is formed along the suction side and hence the longer low pressure side between the conventional outer shell 601 and the conventional inner shell 610. Respectively, a conventional further cooling channel 603 is formed along the shorter high pressure side between the conventional outer shell 601 and the conventional inner shell 610. The conventional inner shell 610 comprises a conventional fluid outlet at the nose section of the conventional inner shell 610 such that cooling fluid is ejected from the conventional inner shell 610 into the conventional cooling channels 602 and the conventional further cooling channels 603, respectively.
In particular, the impingement tube (conventional inner shell 610) and the airfoil (conventional outer shell 601), respectively, comprise the longer low pressure side and a shorter (with respect to the longer lower pressure side) high pressure side. Hence, more mass flow of cooling fluid on the shorter high pressure side flows through the conventional further cooling channels 603 than through the conventional cooling channels 602 along the longer low pressure (suction) side. This results in unequal cooling efficiency and leads to hot metal temperatures in some regions and cool metal temperatures in others. The cooling fluid is drained of through a conventional outer fluid outlet 605 which is formed at a tail section of the conventional outer shell 601.
FIG. 7 shows a conventional airfoil similar to the conventional airfoil shown in FIG. 5. FIG. 6 shows a conventional airfoil which comprises a separating element 701 and a further conventional fluid outlet 702 for adjusting the mass flow of cooling fluid through the respective conventional cooling channels 602, 603. The conventional fluid outlet 604 is formed in the conventional inner shell 610 such that the cooling fluid streams directly into the further conventional cooling channel 603. Additionally, the further conventional fluid outlet 702 is formed into the conventional inner shell 610 for streaming the cooling fluid directly into the conventional fuel channel 602. The conventional fuel channel 602 and the conventional further cooling channels 603 are separated by the separating element 701 which is installed at the nose section of the conventional inner shell 610 and the conventional outer shell 601. Hence, the respective conventional cooling channels 602, 603 are sealed from each other such that the injected cooling fluid into the respective cooling channels 602, 603 is exactly definable. However, complex control mechanisms and the plurality of conventional fluid outlets 604, 702 are necessary and the efficiency of the cooling compromised.
EP 2 628 901 A1 discloses a turbine blade with an impingement cooling. Flow channels are formed between an impingement tube and an outer wall of an airfoil. The impingement tube comprises a plurality of inlet holes for injecting a cooling fluid into the flow channels. Additionally, a blocking element is installed within a flow channel for directing the cooling fluid within the flow channel.
EP 2 573 325 A1 discloses a further impingement cooling for turbine blades or vanes. An impingement tube is installed within a hollow airfoil, wherein flow channels are formed between the impingement tube and the hollow airfoil. The impingement tube comprises a plurality of through holes.
Downstream of the impingement tube, a first impingement device is installed, wherein the cooling fluid flows through the flow channels and further against the first impingement device. The first impingement device comprises again a plurality of through holes through which the cooling fluid is flowable.